1. Field of the Invention
The present invention relates to a rotary expansible chamber device of the epitrochoidal or hypotrochoidal or Wankel type and, more particularly, to means for affording an increased driveshaft diameter for such rotary devices.
2. The Prior Art
Rotary devices of the type to which the present invention may be applied generally comprise a housing defining an epitrochoidal cavity, a rotor member within the cavity and movable therearound in a planetating fashion, and a driveshaft member having an eccentric lobe means fitted thereon about which the rotor rotates. Spaces between peripheral profile surfaces on the rotor and cavity wall surfaces serve to define fluid working chambers in such rotary devices. The working chambers may be subjected to expansion forces, in which case movement of the rotor serves to power the driveshaft, such as in the case of internal combustion or steam engine usage. Alternatively, the driveshaft may serve to rotate the rotor in its housing, such as where rotary devices used as a compressor.
Epitrochoidal rotary devices may be divided into two groups referred to as inner envelope and outer envelope types. In an inner envelope configuration, the profile of the housing cavity is an epitrochoidal curve and the peripheral profile of the rotor is the inner envelope of the epitrochoidal curve. In an outer envelope device, the rotor profile is an epitrochoidal curve and the housing cavity profile is the outer envelope of that curve. The working chambers may be sealed by means including seal rings along the side surfaces of the rotor and axially extending apex seals positioned along apex or intersection lines between adjoining peripheral faces on the envelope curve surface.
In a conventional inner envelope epitrochoidal rotary device, rotation of the rotor about the eccentric lobe portion and relative rotation of the driveshaft are controlled by phasing gear mechanisms. Such phasing gear mechanisms include a ring gear fixed and rotatable with the rotor and a pinion gear fixed with respect to the device housing as shown in U.S. Pat. No. 3,881,847. As a result of engagement between the ring and pinion gears, the rotor is caused to rotate about the eccentric lobe portion during its revolution about the axis of the driveshaft. The relationship between the ring and pinion gears is such as to insure continuous contact between each of the apices of the envelope working member and the peripheral profile surfaces of the epitrochoid member.
Conventional practice has been to provide the two phasing gears with a specific gear ratio relationship which in turn has effectively limited driveshaft diameters. By limiting the driveshaft diameter, one correspondingly limits torque output from or input to the rotor of the expansible chamber device. For example, a conventional epitrochoidal rotary mechanism having an epitrochoidal cavity with two opposed concave lobe portions and a rotor with three apices requires the pitch diameter of the ring gear to be six times the rotor eccentricity, which is the distance between the axial center line of the driveshaft, and the axial center line of the rotor, and the pitch diameter of the pinion gear to be four times the same eccentricity. Because of the above necessary relationship, the ratio of ring gear pitch diameter to that of the pinion gear has heretofore always been provided as 3:2. In other words, the ring gear pitch diameter is one and one half times larger than the pinion gear pitch diameter and has one and one half times as many gear teeth. Because the driveshaft of epitrochoidal rotary units must pass through the inside of the pinion gear, these prior art rotary devices are limited to having a power shaft with a diameter less than the pitch diameter of the pinion gear.
In addition to limiting the torque that can be handled by the driveshaft for a conventionally constructed epitrochoidal rotary device, a driveshaft of limited diameter is more subject to radial force bending as a result of rotor forces, thus producing undesirable vibrations in the rotary unit. Bending of the driveshaft can cause the pinion gear to break and may lead to a high degree of wear in the pinion gear bearing. A conventionally designed driveshaft may further result in the use of journal bearing means which may be of inadequate area to carry loads imposed by the rotor.
Thus, there is a need in the art for an epitrochoidal rotary unit construction having a driveshaft with larger diameters than heretofore possible. With the structure of the present invention, pitch diameter of the pinion gear in the above-described rotary mechanism can be significantly increased without regard to design constraints dictated by the conventional relationships between the ring and pinion gear pitch diameters and rotor eccentricity. As a result of this permitted increase in pinion gear diameter, the driveshaft can also be increased.